You haven't given the model number, however, most were three cylinder two strokes. Look for the simple things first. All the throttle linkage there? When you open the throttle, do the linkages all move on the three carburetors and do the throttle plates open wide? There is linkage that goes up to the timing mark on the flywheel, the linkage should move the little arrow forward when you open the throttle. If all this is there and moving as it should, your problem could lie in fuel supply. If the engine has sat for any length of time, the fuel will be stale and may have gummed up some of the internal passages, within the carbs themselves. You will need to remove and overhaul them. It may also be your fuel pump. You can confirm that by pumping the primer bulb with the throttle open, if you now get lots of power then your fuel pump is not providing enough fuel to fill the carburator bowls. You will need to replace the pump. Check the Fuel filter as well.